The present disclosure relates generally to the field of measuring electrical signals from living subjects (e.g., electrical signals indicative of brain activity and/or heart activity) and providing electrical signals to living subjects (e.g., for neurostimulation or muscle stimulation). In particular, the present disclosure relates to systems, devices, and methods for calibrating the connection between the electrode(s) of such measurement and/or stimulation devices and the tissue of the living subject, typically skin.
The ability to measure signals from a living subject (e.g., those relating to the living subject's bodily functions) can be beneficial for many medical and diagnostic applications. Electrical signals from the brain (i.e., electroencephalography (EEG) signals) can be measured to ascertain brain activity related to abnormal brain function, to monitor spatial and/or temporal progression of brain disease, to aid surgical or nonsurgical intervention by localizing disease-sites in the brain, to monitor brain activity of a healthy subject or a subject of unknown health status when the subject experiences a variety of stimuli and lack of stimuli, etc. Electrical signals from the heart (i.e., electrocardiography (ECG or EKG) signals) can be measured to determine the rate and rhythm of heart beats, the size and position of the heart chambers, the presence of any damage to the cardiac and/or myocardial tissue, the effect of cardiac drugs, the function of cardiac pacing devices, etc. Electrical signals from skeletal muscles (i.e., electromyography (EMG) signals) can be measured to determine medical abnormalities with the skeletal muscles, their activation levels, their recruitment order, to analyze the biomechanics of movement, etc.
The ability to deliver electrical signals to a living subject can also be beneficial for many medical and therapeutic applications. Electrical signals may be delivered to the heart to pace the rate and rhythm of heart beats, and in some cases, for defibrillation of the heart. Electrical signals may be applied to various parts of the nervous system to upregulate and/or downregulate various nerve and nerve-related functions. For example, the spinal cord may be stimulated to treat pain, facilitate injury rehabilitation, restore cardiac function, and lower blood pressure, among other indications. The peripheral nerves may also be stimulated to treat pain, facilitate injury rehabilitation, treat incontinence, and lower blood pressure, among other indications. Electrical signals may be delivered to the skeletal muscles to diagnose responsiveness, facilitate injury rehabilitation, accelerate muscle recovery, improve metabolism, tone skeletal muscle tissue, and as an alternative to weight-bearing exercise, among other purposes. In some cases, the electrical signals delivered may be varied in accordance with other electrical signals measured to provide a form of feedback therapy.
The measurement of electrical signals from a living subject and the delivery of electrical signals are often performed through connection(s) between measurement and/or stimulation electrode(s) and tissue of a patient. In many cases, the connection will be between the skin and the electrode(s). For example, EEG headsets contact EEG electrodes with the scalp of the subject, ECG electrodes are typically contacted to skin on the chest of a subject, EMG electrodes are typically contacted to skin over the target skeletal muscles, and, in some cases, nerves and muscles may be stimulated externally from external electrode(s) contacting skin adjacent the target nerves and/or muscles. The connection between the electrode(s) and skin may not always be ideal for many reasons—such as skin moisture and quality not being ideal for electrode contact, the presence of hair, the presence of regions of thickened and/or hardened skin, the presence of dirt, undesired fluids, or other residue, to name a few examples. Hence, the electrode-to-skin connection may often need to be assessed so that, if appropriate, a medical professional may re-position the electrode, clean the skin and/or electrode, or otherwise re-adjust the connection as needed to have a more ideal electrode connection for the intended measurement and/or diagnosis. In other cases, the connection will be between the electrode(s) and other tissue. For example, the connection may be between dura mater in the epidural space and the electrode lead(s) for spinal cord simulators, between the pacing lead(s) and cardiac tissue for pacing devices, the electrode(s) and skeletal muscle tissue for skeletal muscle stimulators, etc. Connection quality between the electrode(s) and the tissue may again be important to obtain high quality measurements and/or provide the stimulation at the desired levels.
In many cases, the connection between measurement or stimulation electrode(s) and tissue of the subject is assessed before measurement and/or stimulation. Measurement and/or stimulation, in some cases, however, may be long-term and continuous. For example, measurements and/or stimulation may be undertaken for at least 30 minutes, at least an hour, at least a day, or at least a week or more in many applications. And, connection quality may deteriorate or at least vary over the long measurement and/or stimulation time period. Many currently used connection quality assessment methods, however, cannot determine connection quality while measurement and/or stimulation are occurring. For example, many connection quality assessment methods depend on the use of a further reference electrode and/or reference current, which in many cases cannot be present when measurement and/or stimulation are undertaken.
There are therefore needs for improving the way the connection quality between the electrodes of various measurement or stimulation devices is assessed. There are also needs for connection quality assessments methods that are usable concurrently with measurement and/or stimulation, so that electrode connections can be re-adjusted as necessary throughout the desired measurement and/or stimulation time period, the measurement and/or stimulation can be dynamically adjusted based on the current connection quality, the measurement and/or stimulation signal can be recorded along with connection quality assessment to provide signal recordings with more data points for later analysis, to name a few desirable purposes.